External hard disk drives (Transcend, LaCie, Buffalo, Adata, Toshiba, Seagate, WD, etc.) are usually available as pre-assembled integrated products, but may be also assembled by combining an external enclosure (with USB or other interface) with a separately purchased drive. They are available in 2.5-inch and 3.5-inch sizes; 2.5-inch variants are typically called portable external drives, while 3.5-inch variants are referred to as desktop external drives. “Portable” drives are packaged in smaller and lighter enclosures than the “desktop” drives; additionally, “portable” drives use power provided by the USB connection, while “desktop” drives require external power bricks.

Unless External hard disk has serious physical damage. The most important reminder is that serious physical damage is a low probability event and the worst result.

If data loss occurs due to not formatted, not recognized, not working, not showing up, power failure, logical damaged, not detected in bios, a successful recovery must ensure that the deleted data is not over-written.